may be made inside every one knows; how adroitly hidden it may be by external decorations of moss and lichen is familiar to every nest-hunter. The smaller birds usually build the more beautiful nests, and every variety occurs, from the comparatively careless hole in the sand made by the ostrich to the skilfully suspended and neatly fashioned nest of the tailor-bird. It must be noticed that habits vary considerably, as the very diverse nests built in different circumstances by falcon, eagle, heron, etc., well illustrate. Nests are shifted to suit food-supply, and vary in structure according to the available material. And again, since nest-building is obviously an acquired habit, which gradually rewarded the species in the greater success of both parent and offspring during breeding time, it is natural to find it dispensed with in many cases where the nature of the situation rendered no actual nest necessary, or where the birds for some other reason have never learned the habit. Some sea-birds, like the auk, simply lay on the rocky ledges of their haunts; some ground-birds simply deposit their eggs on the bare soil. Burrowed holes are made by sand-martins, bee-eaters, penguins, kingfishers, and many others. The prairie-owl, living in the burrows of the prairie-dog and of the armadillo, is a well-known example of peculiar habit, and in the first case of curious partnership. Ground nests, generally of the simplest character, with rough and scanty accumulation of nest material, are made by swans, ducks, geese, fowls, gulls, waterhens, corncrakes, etc. Mud nests, constructed from damp earth, are well illustrated by the house-swallows, blue-creeper, flamingo, etc. The common singing thrush is well known to make a firm nest of clay and cow-dung mixed with moss. Carpenter-nests, formed with more or less preparation in the holes of trees, are used by woodpeckers and a few other arboreal birds. Platform nests, simply consisting of flat seats, are formed by the ring and turtle doves, by eagles, storks, and cranes. In some parts of the Continent the flat nests formed by the storks on the tops of buildings are familiar enough objects. Basket nests are such loosely interwoven constructions of grass, stems, twigs, etc., as are made by the crows, missel-thrushes, and most singing birds. The green weaving birds (Ploceus pensilis) hang their loosely woven nests, with downward directed opening, on the Madagascar trees. The South African republican birds (Philitærus socius) form hundreds of hanging nests on the branches, under the shelter of a common thatch. Woven nests are the more delicately constructed and really woven constructions of wool, hair, bark, grass, etc., which are made by such birds as the goldfinch, the Baltimore bird, and very many others. Sewed nests, composed of leaves sewed together by the beak as needle, are well illustrated by various species of Icterus, and by the Indian tailor-bird (Orthotomus bennetii). Felt-work nests are woven from